Fuel hose and method of producing thereof

ABSTRACT

A fuel hose comprising an outer rubber layer wherein polysulfide is crosslinked so that polysulfide bonding density is not less than 4x10-5 mol/cm3 and acrylonitrile-butadiene rubber having a carboxyl group is contained, and an inner polyamide resin layer which is laminated on the inside face of the outer rubber layer and bonded thereon by heat treatment. Since the polyamide resin powder is melted by the heat treatment and the polysulfide bonding decomposes so that the resultant residue after decomposition combines with polyamide molecules, resulting in a direct and strong bonding of the outer rubber layer and the inner polyamide resin layer. Moreover, since the special acrylonitrile-butadiene rubber is mixed therein, it is possible to set up the heat treatment condition at a rather mild one.

TECHNICAL FIELD

This invention relates to a fuel hose which is used in the fuel pipingsystems of automobiles and the like and a method of producing thereof.

BACKGROUND OF THE INVENTION

Heretofore, as a fuel hose which is used in the fuel piping systems ofautomobiles and the like, a single-layer rubber hose comprising NBR·PVCrubber (a mixture of acrylonitrile-butadiene rubber andpolyvinylchloride) superior in gasoline resistance and impermeability togasoline has been well known. However, it is a current situation thatsuch a single-layer hose cannot meet the recent severe regulations onimpermeability to gasoline. In such a situation, to satisfy severerconditions, a hose comprising the above outer rubber layer and an innerfluoro rubber layer which is formed on the inside face of the outerrubber layer was developed and has been employed in some fields.

However, since the hose having the inner fluoro rubber layer has adefect of a high cost in spite of its excellent performance, such a hosehas not been generally employed. In the meantime, it is proposed thatthe inner layer be formed by replacing the fluoro rubber with polyamideresin which is more inexpensive.

The polyamide resin has superior properties in gasoline resistance andimpermeability to gasoline. However, since it shows a bad adhesiveproperty with an outer rubber layer, it is required to apply adhesive onthe inside face of the outer rubber layer to laminate these two layers.There causes a problem especially in a filler hose which functions toconnect a hose end with the other material. Namely, the filler hose isoften formed into a smooth faced and curved shape shown in FIG. 1 orinto an accordion shape shown in FIG. 2 for wide adoptability. In casethat a hose is formed into such a special shape, it is difficult toapply adhesive evenly on the inside face thereof and also a dry processafter the application of the adhesive is required, resulting in a morecomplicated process. Further, there is the anxiety that adhesive solventmay aggravate environment. Therefore, it is strongly demanded toestablish a method of producing an inexpensive fuel hose easily bylaminating the inner polyamide resin layer on the inside face of theouter rubber layer without applying adhesive therebetween.

SUMMARY OF THE INVENTION

Under these circumstances, it is an object of this invention to providea fuel hose comprising an outer rubber layer and an inner polyamideresin layer laminated on the inside face of the outer rubber layerwithout applying adhesive therebetween and a method of producingthereof.

To accomplish the above object, a first gist of the invention relates toa fuel hose comprising an outer rubber layer wherein polysulfide iscrosslinked so that polysulfide bonding density is not less than 4×10⁻⁵mol/cm³ and acrylonitrile-butadiene rubber having a carboxyl group iscontained, and an inner polyamide resin layer which is laminated on theinside face of the outer rubber layer and bonded thereon by heattreatment. A second gist of the invention relates to a method ofproducing a fuel hose which comprises:

a step cf preparing an outer rubber layer wherein polysulfide iscrosslinked so that polysulfide bonding density is not less than 4×10⁻⁵mol/cm³ and acrylonitrile-butadiene rubber having a carboxyl group iscontained,

a step of laminating polyamide resin powder on the inside face of theouter rubber layer,

a step of forming an inner polyamide resin layer by heat treatment onthe laminate of the outer rubber layer and the inner polyamide layer,and at the same time bonding the laminate.

Namely, inventors of the present invention have conducted a series ofstudies on various rubber materials to be employed for the outer rubberlayer in order to find out such an optimum material that showspreferable properties in being banded with polyamide resin withoutadhesive. As a result, they found out that when the outer rubber layeris formed by the rubber wherein the crosslinking density of polysulfidebonding (--Sx--, x≧3) is not less than 4×10⁻⁵ mol/cm³, and polyamideresin powder is laminated thereon and heat treated, the polyamide resinpowder is melted so as to be formed into an inner layer by the heattreatment and the polysulfide bonding decomposes so that the resultantresidue after decomposition combines with polyamide molecules, resultingin a direct and strong bonding of the outer rubber layer and the innerpolyamide resin layer. However, since there is a possibility that theouter rubber layer may thermally cure according to heat treatmentconditions so that elasticity or flexibility of thus obtained fuel hosemay be deteriorated, further studies have been conducted on a method bywhich adhesive strength between the outer rubber layer and the innerpolyamide resin layer can be sufficiently retained even in a relaxedheat treatment condition. As a result, they reached the presentinvention by their finding that the above problem can be solved ifacrylonitrile-butadiene rubber (just abbreviated to "NBR" hereinafter)having a carboxyl group is contained into the rubber in which thepolysulfide bonding is adjusted so that crosslinking density is not lessthan 4×10⁻⁵ mol/cm³. In addition, if rubber is vulcanized by a sulfurbased vulcanization accelerator, the bridge structure may formmonosulfide bonding (--S--), disulfide bonding (--S₂ --) and polysulfidebonding (as shown hereinbefore). It is general that polysulfide bondingdensity is adjusted at a minimum level to the utmost from a viewpoint ofheat resistance as rubber products for automobiles. On the other hand,the polysulfide bonding density is adjusted at such a high level asgenerally unbelievable in the present invention, as mentioned above,from a viewpoint of adhesive property with the inner polyamide resinlayer, the heat resistance of rubber can be retained by decomposing thepolysulfide bonding with heat in the heat treatment.

Further, it is preferable to employ a thiazole based vulcanizationaccelerator as a vulcanization accelerator to be mixed in rubbercompound for forming the outer rubber layer to increase the polysulfidebonding density as mentioned above.

Furthermore, the polysulfide bonding density in the vulcanization rubbercan be measured by a chemical reagent treatment method in accordancewith "Determination of Crosslink Density and Vulcanizate Structure"(Monsanto, Rubber Chemicals, July 1983) and a swelling pressure methodin accordance with "Test Method Development for Bridge StructureAnalysis by a Swelling Pressure Method, No.1 report" (BridgestoneCorporation, Japanese Rubber Association Organ Vol. 60, No. 5, 1987).

Now, the present invention is described in detail.

The fuel hose of the present invention comprising the outer rubber layerand the inner polyamide resin layer which is integrated into the outerrubber layer without adhesive can be, for example, produced as follows.First of all, a rubber material, NBR having a carboxyl group, avulcanization accelerator, a plasticizer and the like are mixed andadjusted for the outer rubber layer, and then such a mixture is put intoan injection molding machine or is vulcanized after extrusion molding orthe like so as to form the outer rubber layer. Secondly, polyamide resinpowder is laminated on the inside face of the outer rubber layer andsubsequently heat treated so that the polyamide resin powder is meltedand integrated with the outer rubber layer. Thus, the fuel hose as anobject can be obtained.

In the above method, NBR·PVC rubber is optimum as a rubber material forforming the outer rubber layer from a viewpoint of gasoline resistanceand impermeability to gasoline. However, this is not critical and anyother rubber material may be employed only if it can be vulcanized withsulfur. For example, there are acrylonitrile-butadiene rubber (NBR),polychloroprene rubber (CR), ethylene-propylene copolymer rubber (EPDM)and the like.

Further, as a vulcanization accelerator, any conventional type which hasbeen well known heretofore may be employed, however, it is required thatthe crosslinking density of the polysulfide bonding caused byvulcanization be increased to not less than 4×10⁻⁵ mol/cm³. For thisreason, it is preferable that a thiazole based vulcanization acceleratoras shown in the following general formula (1). Especially,dibenzothiazyl disulfide as shown in the following general formula (2)is most preferable. Furthermore, on condition that the thiazol basedvulcanization accelerator is mainly mixed, the addition of the othervulcanization accelerator(s) than the thiazol based vulcanizationaccelerator results in the same effect. ##STR1##

Furthermore, as a vulcanizing agent, a plasticizer or the like, which iscombined with the rubber material and the vulcanization accelerator,those which have been heretofore employed for forming an outer rubberlayer may be appropriately adopted.

Still further, a great characteristic of the present invention is to mixNBR having a carboxyl group into the rubber composition for forming theouter rubber layer. Namely, the effect of the sufficient adhesivestrength between the outer rubber layer and the inner polyamide resinlayer can be obtained by mixing the specific NBR therein even though theheat condition for melting the outer rubber layer and the innerpolyamide resin powder is set up at a rather mild condition.

The NBR having a carboxyl group may be obtained by polymerizingacrylonitrile monomer, butadiene monomer and monomer having carboxylgroup (just abbreviated to "carboxyl group monomer" hereinafter) as aternary component.

As the carboxyl group monomer, there are acrylic acid, methacrylic acidand the like, which may be employed solely or in combination of two ormore. It is preferable to set up its mixing ratio at 1 to 15% by weight.In case of less than 1%, the effect of improving the above adhesivestrength is poor, while in case of over 15%, there is a tendency that asealing property decreases due to deterioration of permanent set infatigue of rubber in spite of sufficient improvement in adhesivestrength. In addition, the mixing ratio of the NBR having carboxyl groupis preferably set up at 2 to 15 parts by weight (just abbreviated to"parts" hereinafter) based on 100 parts of rubber material such asNBR·PBC rubber and the like. In case of less than 2 parts, the effect ofimproving the adhesive strength is poor, while in case of over 15 parts,there is a tendency that a sealing property decreases due todeterioration of permanent set in fatigue of rubber in spite ofsufficient improvement in adhesive strength.

In the meantime, as polyamide resin for forming the inner layer, thereare nylon 6, nylon 11, nylon 12, nylon 6·10, nylon 6·12, nylon 6/66copolymer, nylon 6/12 copolymer and the like. It is not specificallylimited, however, nylon 11 is most preferable because it is superiorboth in gasoline permeability and flexibility. Further, it is possibleto employ a mixture of the polyamide resin and a plasticizer orelastomer, or a copolymer of the polyamide resin and polyether orpolyester.

Besides, it is preferable to set up a molding temperature at 160° C. anda molding time for 5 to 10 minutes as conditions for molding an outertubular rubber layer, which depends on a tube shape, thickness and thelike, when employing an injection molding machine.

Furthermore, as a method for laminating polyamide resin powder on theinside face of the molded outer rubber layer, it is preferable to attachpolyamide resin powder thereon by electrostatic attraction caused whenthe polyamide resin powder is positively or negatively charged. Inaddition, a various painting methods such as a powder fluid coatingmethod, a spray coating, an internal dip coating method, an electrodeposition and the like.

Still furthermore, as a heat treatment for melting the polyamide resinpowder so as to be integrated with the outer rubber layer, any heatingmeans is acceptable. For example, an oven can be employed. It ispreferable to set up a heating temperature at 200° to 220° C. and aheating time for 10 to 30 minutes, which are rather mild conditions.This is because the hardness of thus obtained rubber outer layerincreases so as to worsen elasticity and flexibility thereof underseverer conditions. Additionally, when the NBR having a carboxyl groupis not mixed, adhesive strength between the outer rubber layer and theinner polyamide resin layer tends to weaken under such mild heattreatment conditions. On the other hand, sufficient adhesive strengththerebetween can be obtained due to the addition of the NBR having acarboxyl group in the present invention.

Besides, thus obtained fuel hose may be in any shape. According to thepresent invention, it is not necessary to apply adhesive on the insideface of the outer rubber layer so as to be bonded with the polyamideinner layer. Therefore, it is especially convenient for figures such asa curved shape shown in FIG. 1 or an accordion shape shown in FIG. 2. Itis most preferable that the present invention applies to filler hoseswhich are formed into such complicated figures.

In thus obtained fuel hose, the polyamide resin powder is melted by heattreatment after being laminated and strongly adhered on the inside faceof the outer rubber layer. Heretofore, there has been a problem ofdelamination caused by uneven coating of adhesive when laminating anouter layer and an inner layer with an adhesive. However, according tothe present invention, there is no delamination caused, resulting inexcellent quality. The polysulfide bonding formed in high density on theouter rubber layer decomposes by the heat treatment and the resultantresidue after decomposition combines with molten polyamide resin so thatthe polysulfide bonding density decreases, which results in sufficientheat resistance of the outer rubber layer. Moreover, since it ispossible to set up mild heat treatment conditions for melting thepolyamide resin powder, the outer rubber layer may not thermally curedso that a hose superior in elasticity and flexibility can be obtained.

EFFECTS OF THE INVENTION

As mentioned before, the fuel hose of the present invention is thelaminate of the outer rubber layer and the inner polyamide resin layerand is more inexpensive than a conventional type having an inner fluororubber layer. Further, since the outer rubber layer and the innerpolyamide resin layer are laminated directly without adhesive,delamination may not be caused, resulting in superior quality. Moreover,since the heat treatment can be set up at mild conditions, elasticity orflexibility of the hose may be retained without heat curing of the outerrubber layer. In addition, according to the present invention, therebecomes no necessity of adhesive, required for bonding the outer layerand the inner layer heretofore, so that a process for coating adhesiveand a dry process after the application of the adhesive are unnecessary,resulting in an easier and more hygienical manufacturing process of theabove fuel hose. Furthermore, since it is possible to set up the heattreatment for melting the polyamide resin powder at mild conditions,reduction of energy consumption can be realized by shortening the heattreatment time and controlling the heat treatment temperature. Stillfurthermore, the production efficiency can be improved by shortening theheat treatment time. Still even furthermore, according to the presentinvention, filler hoses and the like which are formed into complicatedfigures can be produced easily. Additionally, the above effects can beconspicuously obtained if a thiazole based vulcanization accelerator isemployed as a vulcanization accelerator for forming the outer rubberlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of a fuel hose according to thepresent invention and

FIG. 2 illustrates another embodiment of a fuel hose according to thepresent invention.

The present invention will now further be described by reference to thefollowing illustrative examples.

EXAMPLES 1 TO 7 AND COMPARATIVE EXAMPLES 1 TO 2

First of all, each rubber composition was prepared in accordance withthe following tables 1 and 2. Then, each composition was injectionmolded at 160° C. for 5 minutes so as to be formed into accordion fuelhoses (A to G) at 35 mm of inside diameter, in 4 mm thickness and 200 mmlength. Each crosslinking density of polysulfide bonding of thusobtained hoses was measured in accordance with the above measuringmethod. The results are shown in the following tables 3 to 5.

                  TABLE 1                                                         ______________________________________                                                       (Parts)                                                                       A     B       C       D                                        ______________________________________                                        NBR.PVC *1       100     100     100   100                                    Stearic acid     0.7     0.7     0.7   0.7                                    Zinc oxide       3       3       3     3                                      Carbon black *2  75      75      75    75                                     Calcium carbonate                                                                              20      20      20    20                                     Ether ester plasticizer                                                                        30      30      30    30                                     N-phenyl-N' isopropyl-p-                                                                       2       2       2     2                                      phenylenediamine                                                              NBR having a carboxy group                                                    A *3             5       10      15    --                                     B *4             --      --      --    10                                     Sulfur           1.5     1.5     1.5   1.5                                    Vulcanization accelerator                                                     Thiazole base                                                                 MBTS *5          0.75    0.75    0.75  0.75                                   CBS *6           --      --      --    --                                     Thiuram base                                                                  TETD *7          --      --      --    --                                     TMTD *8          --      --      --    --                                     ______________________________________                                         *1 NBR/PVC = 70/30 (ratio by weight)                                          *2 Carbon black SRF (a product of Tokai Carbon Co., Ltd.)                     *3 Amount of acrylic monomer: 7% by weight                                    *4 Amount of acrylic monomer: 12% by weight                                   *5 Dibenzothiazyl disulfide                                                   *6 Ncyclohexyl-2-benzothiazylsulfenamide                                      *7 Tetraethylthiuramdisulfide                                                 *8 Tetramethylthiuramdisulfide                                           

                  TABLE 2                                                         ______________________________________                                                           (Parts)                                                                       E     F       G                                            ______________________________________                                        NBR.PVC *1           100     100     100                                      Stearic acid         0.7     0.7     0.7                                      Zinc oxide           3       3       3                                        Carbon black *2      75      75      75                                       Calcium carbonate    20      20      20                                       Ether ester plasticizer                                                                            30      30      30                                       N-phenyl-N' isopropyl-p-phenylenediamine                                                           2       2       2                                        NBR having a carboxyl group                                                   A *3                 10      --      10                                       B *4                 --      --      --                                       Sulfur               0.5     1.5     0.5                                      Vulcanization accelerator                                                     Thiazole base                                                                 MBTS *5              --      0.75    --                                       CBS *6               1.2     --      --                                       Thiuram base                                                                  TETD *7              2.1     --      --                                       TMTD *8              --      --      2.0                                      ______________________________________                                         *1 NBR/PVC = 70/30 (ratio by weight)                                          *2 Carbon black SRF (a product of Tokai Carbon Co., Ltd.)                     *3 Amount of acrylic monomer: 7% by weight                                    *4 Amount of acrylic monomer: 12% by weight                                   *5 Dibenzothiazyl disulfide                                                   *6 Ncyclohexyl-2-benzothiazylsulfenamide                                      *7 Tetraethylthiuramdisulfide                                                 *8 Tetramethylthiuramdisulfide                                           

Then, polyamide resin powder was electrostatically coated in 0.2 mmthick on each inside face of the above 7 kinds of the rubber hoses (A toG) as an outer rubber layer in accordance with the conditions shown inthe following tables 3 to 5. Such electrostatic coating was conducted bypositively charging the polyamide resin powder by corona discharge at 60kV/10 μA. Thus obtained laminates were heat treated in accordance withconditions also shown in the following tables 3 to 5, so that fuel hosesas objects were obtained. The smooth faced parts of thus obtained fuelhoses were cut out axially with 25 mm width in a ring state and were cutopen axially, and then each circumferential breakaway strength wasmeasured. Further, rubber hardness of each outer rubber layer after theheat treatment was measured in accordance with JIS A and its change wassought. In addition, compression set, flexibility and gasolinepermeability of each fuel hose were valued in accordance with thefollowing methods. These results are shown also in the following table 3to 5.

Compression set!

Compression set (%) of each sample was measured after 100° C.×22 hoursin accordance with JIS K6301.

Flexibility of hoses!

When one end of a hose was fixed while the other end was strained by 200mm in the direction of 90° to the axis, the load (N) was measured. Incase that the load was not more than 700N, the evaluation was ∘. In casethat the load was from 700 to 900N, the evaluation was ⊚.

Impermeability to gasoline!

Fuel C was sealed in a hose as a pretreatment and was let it stand for40° C.×168 hours. Subsequently, Fuel C was sealed again and was let itstand with 40° C. maintained.

Weight decrease was measured every 24 hours, up to 72 hours. In casethat the weight decrease was 0.1 g for 1 piece per day, the evaluationwas ∘. In case that the weight decrease was 0.1 g to 0.2 g for 1 pieceper day, the evaluation was ◯.

                  TABLE 3                                                         ______________________________________                                                   EXAMPLES                                                                      1      2        3        4                                         ______________________________________                                        Outer rubber layer                                                                         A        B        C      D                                       Polysulfide bonding                                                                        8 × 10.sup.-5                                                                    8 × 10.sup.-5                                                                    8 × 10.sup.-5                                                                  8 × 10.sup.-5                     density (mol/cm.sup.3)                                                        Material of an inner                                                                       nylon    nylon    nylon  nylon                                   polyamide resin layer                                                                      11       11       11     11                                      Heat treatment                                                                conditions:                                                                   210° C. × 20 minutes                                             Change of rubber                                                                           +3       +3       +4     +3                                      hardness (JIS A)                                                              Delamination strength of                                                                   rubber   rubber   rubber rubber                                  an outer layer and an                                                                      break    break    break  break                                   inner layer (N/mm)                                                            Compression set (%):                                                                       43       44       50     43                                      100° C. × 22 hours                                               Hose flexibility                                                                           ⊚                                                                       ⊚                                                                       ⊚                                                                     ⊚                        Impermeability to                                                                          ⊚                                                                       ⊚                                                                       ⊚                                                                     ⊚                        gasoline                                                                      ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                                        EXAMPLES                                                                      5      6        7                                             ______________________________________                                        Outer rubber layer                                                                              E        A        A                                         Polysulfide bonding density                                                                     4 × 10.sup.-5                                                                    8 × 10.sup.-5                                                                    8 × 10.sup.-5                       (mol/cm.sup.3)                                                                Material of an inner polyamide                                                                  nylon    nylon 6/66                                                                             nylon                                     resin layer       11       copolymer                                                                              12                                        Heat treatment conditions:                                                    210° C. × 20 minutes                                             Change of rubber hardness (JIS A)                                                               +2       rubber   rubber                                                               break    break                                     Delamination strength of an outer                                                               1.7      rubber   rubber                                    layer and an inner layer (N/mm)                                                                          break    break                                     Compression set (%):                                                                            41       43       43                                        100° C. × 22 hours                                               Hose flexibility  ⊚                                                                       ∘                                                                          ∘                             Impermeability to gasoline                                                                      ⊚                                                                       ⊚                                                                       ∘                             ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                                             COMPARATIVE                                                                   EXAMPLES                                                                      1      2                                                 ______________________________________                                        Outer rubber layer     F        G                                             Polysulfide bonding density (mol/cm.sup.3)                                                           8 × 10.sup.-5                                                                    2 × 10.sup.-5                           Material of an inner polyamide resin layer                                                           nylon    nylon                                                                11       11                                            Heat treatment conditions: 210° C. × 25 minutes                  Change of rubber hardness (JIS A)                                                                    +8       +12                                           Delamination strength of an outer layer                                                              rubber   0.8                                           and an inner layer (N/mm)                                                                            break                                                  Heat treatment conditions: 210° C. × 20 minutes                  Change of rubber hardness (JIS A)                                                                    +3       +2                                            Delamination strength of an outer layer                                                              0.6      0.4                                           and an inner layer (N/mm)                                                     Compression set (%): 100° C. × 22 hours                                                 40       41                                            Hose flexiblity        ⊚                                                                       ⊚                              Impermeability to gasoline                                                                           ⊚                                                                       ⊚                              ______________________________________                                    

From the above results, it is found out that the outer layer and theinner layer of every example were strongly bonded in spite of a shortheat treatment time, resulting in high quality. Among all, it isapparent that examples 1 to 4, which employed dibenzothiazyl disulfideas a vulcanization accelerator and nylon 11 as polyamide resin, showedsuperior performance. On the other hand, comparative example 1, whichdid not contain NBR having a carboxyl group, and comparative example 2,in which crosslinking density by polysulfide bonding is low, showed weakadhesive strength of the outer layer and the inner layer, resulting inlack of practicability.

EXAMPLE 8

16 parts of NBR having a carboxyl group (containing acrylic monomer by7% by weight) were employed for 100 parts of NBR·PVC. A hose wasobtained under the same conditions as those of Example i except for theabove. EXAMPLE 9

The heat treatment condition for the laminate in which polyamide resinpowder was laminated was set at 210° C.×10 minutes. A hose was obtainedunder the same conditions as those of Example 1 except for the above.

The examples 8 and 9 were evaluated in the same ways as those of theabove examples and comparative examples. These results are shown in thefollowing table 6.

                  TABLE 6                                                         ______________________________________                                                             EXAMPLES                                                                      8      9                                                 ______________________________________                                        Change of rubber hardness (JIS A)                                                                    +4       +2                                            Delamination strength of an outer layer                                                              rubber   1.6                                           and an inner layer (N/mm)                                                                            break                                                  Compression set (%): 100° C. × 22 hours                                                 54       43                                            Hose flexibility       ⊚                                                                       ⊚                              Impermeability to gasoline                                                                           ⊚                                                                       ⊚                              ______________________________________                                    

From the above results, it is found out that as the mixing ratio of NBRhaving a carboxyl group increases, compression set value becomes larger,resulting in a tendency of deterioration of permanent set in fatigue. Inaddition, when the heat treatment condition is mild too much, there is atendency that the adhesive property between the outer layer and theinner layer deteriorates.

What is claimed is:
 1. A fuel hose comprising an outer rubber layerhaving a cross-linked structure with a polysulfide bonding density ofnot less than 4×10⁻⁵ mol/cm³ and being formed by sulfur-vulcanizing arubber composition comprising a carboxyl group-containingacrylnitrile-butadiene rubber and an inner polyamide resin layerlaminated on the inside face of the outer rubber layer and integratedthereinto by heat-bonding so that polysulfide bonds of the outer rubberlayer decompose during the heat-bonding and the resultant residue afterdecomposition combines with polyamide molecules of the polyamide resinlayer so as to form a strong bond between the outer rubber layer and theinner polyamide resin layer.
 2. A fuel hose according to claim 1,wherein the rubber composition contains a thiazole vulcanizationaccelerator.
 3. A method of producing a fuel hose comprising an outerrubber layer and an inner polyamide layer laminated on and integrated byheat-bonding to the inside face of the outer rubber layer, whichcomprises:a) forming the outer rubber layer by sulfur-vulcanizing arubber composition comprising a carboxyl group-containingacrylonitrile-butadiene rubber to form a cross-linked structure havingpolysulfide bonding density of not less than 4×10⁻⁵ mol/cm³, b) coatingthe inside of the outer rubber layer with a polyamide resin powder, andc) heating the polyamide resin powder-coated outer rubber layer to meltthe polyamide resin powder and bond the polyamide to the outer rubberlayer, wherein a strong bond between the outer rubber layer and theinner polyamide resin layer is formed by decomposing polysulfide bondsof the outer rubber layer and combining the resultant residue afterdecomposition with polyamide molecules of a molten layer of thepolyamide resin powder.
 4. A method of producing a fuel hose accordingto claim 3, wherein the rubber composition contains a thiazolevulcanization accelerator.